Various pyrazolone derivatives are known as magenta-dye-forming couplers (hereinafter referred to simply as magenta couplers). However, pyrazolone derivatives generally used for photographic light-sensitive materials are 4-equivalent couplers. Such compounds theoretically require the development of four mols of silver halide for forming one mole of a dye by reacting with an aromatic primary amine developing agent. On the contrary, pyrazolones having an active methylene group substituted with a group which can be released by oxidative coupling with an oxidation product of the primary amine developing agent require development of only two mols of silver halide. In addition, the 4-equivalent pyrazolone derivatives have a low color forming efficiency (conversion rate of the coupler into the dye) and generally form only a 1/2 mol or so of the dye per mol of the coupler.
As a means for improving the color forming efficiency by decreasing the amount of silver halide required for development, utilization of 2-equivalent pyrazolone magenta couplers has been proposed.
Examples of pyrazolone derivatives which release an oxygen atom include compounds having an aryloxy group in the 4-position of the 5-pyrazolone group as described in U.S. Pat. No. 3,419,391, and compounds having an alkyloxy group as described in Japanese Patent Publication No. 46453/78.
Examples of pyrazolone derivatives which release a nitrogen atom include compounds having an imidazolyl group, a pyrazolyl group, or a triazolyl group in the 4-position of the 5-pyrazolone group as described in U.S. Pat. Nos. 4,076,533 and 4,241,168, compounds having a pyridonyl group or a 2-oxopiperidinyl group as described in U.S. Pat. No. 4,220,470 and compounds having a sulfonamido group as described in U.S. Pat. No. 4,237,217.
Further, examples of pyrazolone derivatives which release a sulfur atom include compounds having a heterocyclic thio group or an arylthio group in the 4-position of the 5-pyrazolone group as described in U.S. Pat. Nos. 3,227,554 and 4,263,723, Japanese Patent Publication No. 34044/78, compounds having a thiocyano group as described in U.S. Pat. No. 3,214,437 and compounds having a dithiocarbamate group as described in U.S. Pat. No. 4,032,346. These compounds are advantageous in that most of them can be synthesized from 4-equivalent pyrazolone couplers in one step. Also, these compounds are advantageous in view of photographic sensitivity and equivalency. It has been found that compounds having a 2-alkoxyarylthio group in the 4-position of the 5-pyrazolone group have exceptionally superior properties among couplers of the type which release an arylthio group. In addition, magenta color images formed from the couplers having a 2-alkoxyarylthio group have good fastness to light, while the light fastness of magenta color images formed from conventional couplers having an arylthio group is significantly inferior.
However, these 2-equivalent magenta couplers are still insufficient in view of the occurrence of stains (increase in color density in unexposed areas) which are formed by development processing, although they are fairly improved.
The stains occurring in unexposed areas of silver halide color photographic light-sensitive material are undesirable and are a determining factor with respect to whether whiteness of the non-image areas is good or bad. Further, such stains adversely affect the color turbidity of the images and injure the visual sharpness of the images. Particularly, in the case of reflective photographic materials, for example, photographic color papers, the reflective density of the stains is theoretically emphasized several times that of the transmission density. Therefore, the stains are very important factors since even a slight degree of stain will injure the image quality.
Stains in the silver halide color photographic light-sensitive materials are roughly classified into four groups depending on the cause of the stain. First is a stain which is formed after the production of the photographic light-sensitive material and before the processing thereof due to heat or humidity. Second is a stain caused by the development fog of the silver halide. Third is a stain based on color contamination due to color couplers in a development processing solution (for example, aerial fog, etc.) or a stain due to a dye formed by reaction with a coupler of an oxidized developing agent which is formed by oxidation of a developing agent remaining in the silver halide emulsion layer by a bleach solution or oxygen in the air, etc. (for example, bleaching stain, etc.). Fourth is a stain based on changes in photographic materials after development processing with the passage of time due to light, humidity or heat. The present invention relates to stains due to the development processing of photographic materials containing 2-equivalent magenta couplers, i.e., the present invention relates to the third and fourth types of stains described above.
It is unusual to prepare a new solution for every development processing. In practice, the solution is replenished by adding a replenishing developing solution in an amount which depends on the amount of photographic materials developed. Even so, the composition of the solution can not be maintained indefinitely simply by adding components which are consumed by development.
In general, solutions for development processing include a color developing solution, a stopping solution, a bleaching solution, a fixing solution or a bleach-fixing (blixing) solution, etc. Since the processing temperature is maintained at a high temperature such as from 31.degree. C. to 43.degree. C., the compositions of the processing solutions can be changed by several factors. For example, components such as the developing agent, etc., is subjected to decomposition for a long period of time or to oxidation when brought in contact with the air. It is also possible for the components contained in the photographic light-sensitive materials to dissolve out and accumulate in the solution during the processing of the photographic light-sensitive materials. In addition, the processing solution may be transferred into the subsequent baths by becoming attached to the photographic material. Thus, the processing solution becomes a so-called running solution. To eliminate such problems, a replenishment procedure in which chemicals lacking are supplementally added to the solution and a regeneration procedure in which undesirable components are removed are carried out, but even these steps are still not completely sufficient.
Photographic light-sensitive materials containing 2-equivalent magenta couplers have a strong tendency to form stains in the running solution. However, the occurrence of such stains cannot be sufficiently prevented by techniques heretofore known. An example of a somewhat effective method for preventing such stains involves the incorporation of a reducing agent, particularly, an alkylhydroquinone (for example, those as described in U.S. Pat. Nos. 3,935,016 and 3,960,570, etc.) into a photographic light-sensitive material, particularly, an emulsion layer wherein the stains are formed. It is also known that a chroman, a coumaran (for example, those as described in U.S. Pat. No. 2,360,290), a phenol type compound (for example, those as described in Japanese Patent Application (OPI) No. 9449/76), etc. are somewhat effective. Furthermore, a sulfinic acid type polymer is known as being effective as described in Japanese Patent Application (OPI) No. 151937/81. However, these known techniques cannot provide a sufficiently good effect against processing stain due to use of 2-equivalent magenta couplers, and, in particular, to the processing stain owing to the exhausted solution, even though some effect is obtained.
Further, recently an attempt to reduce the replenishing amount is being made in a photofinishing laboratory for the purposes of reduction of wastes. In this case, they may be found an elevation of pH and an increase of the degree of stain occurrence.
Still further, such phenomena are likely found in case that in a small photofinishing laboratory, the control of replenishing amount, etc is not sufficiently achieved.